Excel Pivot Table Function in Power BI: Show values as Difference from

Hi,

I have an Access DB which feed data into ane Excel Data Model and Power BI. This is the weekly reporting cash balances of a couple companies.

In Excel is quite easy to do the calculation I want: "Show Values As", "Difference From" "Previous".

And VOILA!! I've the calculculation i want, which is the difference between the current and the previos column (reporting date):

How is this done in Power BI? I've tried some DAX with no success: CALCULATE + SAMEPERIODLASTYEAR or PARALELL or ALL , ETC.

In advance thanks for your support.

DB can be found at:

https://drive.google.com/open?id=0B4nGHx9e6JNLZWhnakp1LUh5T00 

Oscar